1. Field of the Invention
This invention relates to liquid developers for electrostatic latent image which are used in electrophotography, electrostatic recording, electrostatic printing, and the like. More specifically, this invention relates to liquid developers for electrostatic latent image which are particularly usable in electrophotography comprising the steps of developing an electrostatic latent image and transferring the image so developed to a transferring member.
2. Description of the Prior Art
The characteristics required for a liquid developer for use in electrophotography wherein an electorstatic latent image formed on an insulating layer or a photosensitive layer is wet-developed and the image so developed is transferred to a transferring member (see, for example, Japanese Patent Publication No. 24077/1970 ) may be given as follows: (1) the electrostatic latent image can be developed to provide an image which is of high density, clear, and fogless, (2) the image so developed is not disturbed by pressure applied at transferring step wherein the image is transferred to a transferring member and it is of transferability enough to provide a fully sharp image to the transferring paper, (3) the image transferred to the transferring member is fully fixed and (4) the liquid developer remaining on the insulating layer or the photosensitive layer is easily erasable after transferring so that the surface may be used repeatedly.
Conventional liquid developers for electrophotography have been developed mainly for developing the electostatic latent image formed on the electophotographic photosensitive paper of zinc-binder system. On using them for electrophotography wherein the developed image is transferred to the transferring member, it has been found that they have either of the following disadvantages. That is, they are of so poor transferability that even though an image of fully high density is obtained on the photoconductive or the insulating layer, the transferred image is of low density and of low quality. Furthermore, the fixation of the transferred image on the transferring paper is so poor that the transferred image is easily disturbed by rubbing slightly with a finger tip after drying a carrier liquid of the liquid developer and thus they are of no practical value. In addition, a large amount of toner remains on the insulating layer or the photosensitive layer, arising difficulty in cleaning the surface. The inferiority with time of the developer is so vigorous that it is not applicable to electrophotograpghy of transferring type.